The present invention relates to the production of a non-woven material having high extensibility and comprising polymer fibers using mixtures of amphiphilic block copolymers as compatibilizers for preparing blends as well as their production and use.
Non-woven materials are a class of product which has been known on the hygiene market for many years. Although non-woven materials can basically be produced from all the known types of fibers, only a few polymers have gained acceptance in this market, be it for reasons of technology or price.
The most common material is polypropylene.
There are several reasons for this:                Polypropylene is available in large quantities and different qualities at a favorable price.        Polypropylene is easy to handle in melt-spinning processes.        The non-woven materials which can be produced from polypropylene are satisfactory, on the basis of their properties with regard to application technology, for a number of areas of application in the hygiene market.        
However, non-woven materials of pure polypropylene often do not have the extensibility which is required for non-woven materials in the field of hygiene products. In order to provide a remedy here, for example, elastic polymers are mixed with the polypropylene. Thereby the extensibility of the resulting non-woven materials is in fact improved but the production process is clearly more complicated since the spinning of threads from mixtures of this type is far more difficult than from polypropylene.
An additional polymer used in the field of hygiene is polyethylene. Non-woven materials of this material distinguish themselves by their softness. Non-woven materials of linear polyethylene with low density have high extension properties and outstanding properties with respect to handle, softness, and drape as, for example, is known from U.S. Pat. No. 4,644,045 by Fowells. However, materials of this type have not found commercial acceptance because they do not provide acceptable resistance to abrasion. The bonding of the LLDPE filaments in a spunbonded web with acceptable resistance to abrasion has proven itself very difficult because an acceptable bonding is observed at a temperature just under the point at which the filaments begin to melt and adhere to the calender. Due to this very narrow bonding range and the resulting resistance to abrasion and fuzzing properties, spunbonded LLDPE non-woven materials have not found wide commercial acceptance for the above-mentioned applications.
For reasons of price as well as technology the amount of polyethylene used in the field of hygiene is clearly less than that of polypropylene. In comparison to that, other polymers, such as, for example, polyester, are used even more rarely in the field of hygiene.
The production of non-woven materials using fibers of a blend of polypropylene and polyethylene, especially of HDPE, is known. Due to the incompatibility of the two polymers the presence of a compatibilizer for preparing blends during the preparation process is absolutely necessary to obtain a miscible and spinnable system.
As compatibilizers for preparing blends, copolymers in which polypropylene and polyethylene units are joined to one another in different proportions are used as a matter of priority. In order to ensure sufficient compatibilizing for preparing blends of the non-miscible polymers, additives of these copolymers are required on the orders of magnitude of 10% by weight to 20% by weight relative to the total mixture. However, additives of copolymers on this order of magnitude often lead to undesirable changes in properties which are characterized by the fact that individual properties of the resulting mixture are worse than those properties of pure polypropylene or polyethylene respectively.
For several years, elastic non-woven materials have also found application in the hygiene sector. These non-woven materials distinguish themselves by a clearly higher extensibility vis-à-vis the traditional hygienic non-woven materials of polypropylene or polyethylene. Base materials for the production of these elastic non-woven materials are in most cases elastic block copolymers, for example, on the basis of polyurethane.
Similar tendencies are to be observed with the use of polyolefin elastomers, which are essentially also block copolymers, and most often comprise polypropylene and polyethylene.
Non-woven materials using elastic polyurethanes as well as non-woven materials using polyolefin elastomers are, due to their composition and the complexity of production associated therewith, very costly. From the financial point of view, this is an enormous disadvantage for their use in hygiene products.
There are different approaches to producing non-woven materials with high extensibility which comprise polyethylene.
From WO0034385 a mixture for the production of fibers consisting of polypropylene and a polypropylene/polyethylene copolymer with an improved spinnability and extensibility is known, where the fibers are spun with a fineness between 1 and 50 denier (den). In the mixture 0.1% by weight to 30% by weight of polyethylene with an MFI ≦10 g/10 min (190° C., 2.16 kg), preferably ≦5 g/10 min (190° C., 2.16 kg), and a density between 0.85 g/cm3 and 0.97 g/cm3 are used, where the rest of the mixture consists of polypropylene with an MFI ≧12 g/10 min (230° C., 2.16 kg). The fibers are thermobonded in the temperature range between 127° C. and 137° C. In this case either a polyethylene is used as a copolymer of a polyethylene and an α-olefin with an MFI between 5-10 g/10 min (190° C., 2.16 kg) and a density=0.87 g/cm3 or a homopolymer or copolymer of a polyethylene and an α-olefin with an MFI <5 g/10 min (190° C., 2.16 kg) and a density ≧0.87 g/cm3. The production of the mixtures is done on a co-rotating double-screw extruder. In a subsequent spinning process the threads are stretched via a take-off roller.
In the publication US2004038022 the production of an extensible non-woven material of fibers is disclosed where the fibers were produced from a polypropylene/polyethylene mixture with a polyethylene portion of 0.5-22% by weight and the fibers were consolidated at a bonding temperature which is 15-20° F. under the temperatures at which the reference non-woven materials of pure polypropylene are customarily consolidated. The optimal bonding temperature was determined at a stretching rate of 6% per minute. The extensibility of the claimed non-woven material is at least 20% higher than that of a comparable non-woven material of polypropylene at stretching rates of 10,000 to 11,000% per second.
In this case the following were used:                Polypropylene with an MFI ≧25 g/10 min (230° C., 2.16 kg) as a homopolymer or copolymer with polyethylene and a        polyethylene with a short chain branching distribution index, SCBDI) ≧50% in the form of a copolymer of a ethylene and α-olefin whose MFI ratio MFI10/MFI2≧5.63, where the polyethylene has a density between 0.855 g/cm3 and 0.88 g/cm3 and an MFI between 0.01-10 g/10 min (190° C., 2.16 kg), preferably <5 g/10 min (190° C., 2.16 kg).        
For example, with a non-woven material which has a base weight of 20 g/m2 and fibers with ca. 2 den, 100% extension in the CD direction and 93% extension in the MD direction are achieved with a mixing ratio of polypropylene/polyethylene of 90/10. In this case the mixture was produced on a double-screw extruder without the addition of additives.
The consolidation of the fibers to form a non-woven material was done in this case at temperatures between 132° C. and 154° C.
From WO00/04215 a method for the production of a thermally bonded, highly extensible non-woven material, in particular using core-sheath polypropylene staple fibers is known. The extensibility of the non-woven material is in this case achieved by a special bonding pattern which has been produced by means of a calender.
In U.S. Pat. No. 5,804,286 an extensible textile composite material using a polypropylene/polyethylene blend and a block or graft polyolefin copolymer or terpolymer is claimed, said blend being at least partially miscible with polyethylene and PE.
In U.S. Pat. No. 5,921,973 possibilities for use of extensible, non-elastic non-woven materials are claimed which are contained as components in an elastic composite material. The composite material consists of a layer of non-elastic, extensible staple fibers which were produced from a blend of polyethylene and polypropylene and of an elastic layer in the form of an elastic film. Possibilities for use for the composite material are seen in the area of throw-away products, such as, for example, diapers, incontinence products, and feminine hygiene.
From U.S. Pat. No. 5,616,412 fibers of a mixture of polypropylene and polystyrene are known which have extensions of more than 700% for fiber diameters between 2 and 4 den. The mixture was produced via a double-screw extruder, where the following mixture composition has been chosen:
polypropylene: 90-98% by weight with an MFI of 20 g/10 min and
polystyrene: 2-10% by weight with an MFI of 1.5 g/10 min.
In U.S. Pat. No. 5,322,728 fibers are described from which textile articles with extensibilities up to ca. 100% in the MD direction can be produced which have been spun in the melt-blown as well as in the melt-spinning processes. Clear advantages with regard to the softness and the elastic recoverability were already observed at 50% extension of the textile articles. The textile articles are produced from a copolymer of ethylene and at least one comonomer, where styrene is preferably used as the copolymer, but also propylene. The textile articles thus obtained find application in drapes and articles of clothing.
U.S. Pat. No. 5,494,736 discloses a highly extensible non-woven material which is produced by the fibers laid down preferably being oriented in the CD direction. The bonding surface of the consolidated non-woven material is specified as 8-25% relative to the total surface of the non-woven material. Staple fibers are used which are put in a preferred direction by carding.
From EP1461479/WO03052179 the production of extensible fibers of polymer compositions, preferably containing polyethylene, polypropylene, polyethylene-polypropylene copolymers, are known where the fibers are only stretched to a slight extent. The stretching ratio is <400, preferably <150, and particularly preferably <50. In order to achieve the fiber strengths between 1.5 and 4 dtex customary in spinning fibers, the melt must be pressed through particularly small spinnerets. Diameters of <200 μm, quite particularly preferably <100 μm are specified. In order to be able to produce these fibers, polymers with an MFI, e.g. for polypropylene compositions, of at least 400 g/10 min (230° C., 2.16 kg) are required.
Splittable multi-component fibers for extensible non-woven materials, e.g. of polyolefins, which have an extensibility of over 800%, are disclosed in US20040161994. Their production is done in a melt-spinning process where the resulting fibers are essentially unstretched and thus extensible and splittable. Instead of spinnerets with very small bore diameters, such as, for example, are known from EP1461479, spinnerets with bore diameters are used in US20040161994 which permit the spinning of fibers whose diameter is =40 μm.
Subsequently, the fibers are split in order to obtain those fiber finenesses which are required for non-woven materials in the fields of application such as, for example, throw-away articles in the form of diapers, incontinence products, feminine hygiene articles, or wipes.
An area-measured material in the form of a composite material consisting of a rubber-elastic material of thermoplastic elastomers and a non-woven material is disclosed in US020040166756 and is, for example, suitable for use in throw-away articles. The non-woven material contains non-elastic filaments, e.g. consisting of polypropylene, which are preferably laid out in the MD direction. Perpendicular to this preferred direction the area-measured material has an extensibility of more than 100%.
From US2002039637 non-woven materials were produced from a mixture of polypropylene, polyethylene, and a commercially obtainable compatibilizer for preparing blends in the form of a block or graft copolymer, e.g. of the Catalloy™ copolymer from the Montell company. In this case the compatibilizer for preparing blends is added to between 15% by weight and 30% by weight relative to the total mixture. At peak load, extensions of over 500% were observed in the case of these non-woven materials.
In WO0149908 multi-component fibers are described for the production of non-woven materials with high extensibility. In one embodiment polyolefin mixtures are used where the lower melting polymer forms the dominant continuous phase of the multi-component fiber and the higher melting polymer forms the disperse phase included in the continuous phase. The lower melting polymer is added to the mixture on an order of magnitude of at least 50% by weight relative to the total mixture. For the production of the polymer mixture, for example, a polyethylene with a density of at least 0.945 g/cm3, an MFI >10 g/10 min, and a polypropylene with an MFI of at least 20 g/10 min is used. At peak load, extensions of at least 100% were observed in the case of these non-woven materials.
Also known are extensible non-woven materials from U.S. Pat. No. 5,593,768. The multi-component fibers used in this case comprise a dominant continuous phase and a discontinuous highly disperse phase of at least two different thermoplastic polymers where the highly disperse phase forms elongated fibrillar domains which are oriented in the direction of the fiber axis within the continuous phase of the fiber. In one embodiment the dominant continuous phase is formed by isotactic polypropylene and the discontinuous phase is formed by polyethylene on orders of magnitude between 2.5% by weight to 20% by weight relative to the total mixture. In this case extensions of up to 128% were observed in the non-woven material.
The known approaches to the production of non-woven materials having high extensibility, which comprise polyethylene as a primary constituent of the mixture and polypropylene type [sic] as a secondary constituent, are often very costly and time-consuming. For the preparation of this mixture an intensive energy input is required during the homogenization so that in many cases double-screw extruders must be used.
In order to ensure the processability and, in particular, the spinnability of these incompatible polymers at all, and to impart a sufficient level of properties to the end product in the form of fibers or non-woven materials, compatibilizers for preparing blends in the form of block and/or graft copolymers are necessary in addition, where said block and/or graft copolymers can assume in the case of the previously known compatibilizers for preparing blends, an order of magnitude of approximately 10% by weight to 20% by weight relative to the total mixture, and formulate the end product in a more costly manner.
Time-consuming and thus also more costly are technologies for the production of extensible non-woven materials on the basis of polypropylene, which are based on the use of calendars with special bonding patterns in order to establish definite extension properties in the consolidated non-woven material. The mounting and dismounting of calender rollers as well as the checking and optimization of bonding patterns, which usually has as a consequence the re-embossing of calender rollers, are time-consuming and thus expensive.
Thus, it would be advantageous to have additives for processing mixtures of non-miscible polymers for the production of extensible polymer-fiber non-woven materials which, with regard to their compatibilizing for preparing blends, show a significantly improved effect, and due to this can be dosed at a lower rate and require less effort in preparation.